Transducing head design for microwave assisted magnetic recording

ABSTRACT

A magnetic writer includes a write element having a write element tip and a conductive structure adjacent the write element. The conductive structure includes two conductive elements positioned substantially parallel to one another and separated by an electrically insulating material. Each of the conductive elements carries a time-varying signal to generate an oscillating magnetic field from a displacement current between the two conductive elements, with the oscillating magnetic field being proximate the write element tip and extending parallel to the air bearing surface. A frequency of the oscillating magnetic field is a function of a frequency of the time-varying signal.

BACKGROUND

Hard disc drives (HDDs) typically comprise one or more magnetic media discs (or other magnetic storage medium), each disc having concentric data tracks for storing data. Where multiple discs are used, a stack is formed of co-axial discs having generally the same diameter. A transducing head carried by a slider is used to read from and write to a data track on a given disc. The slider is carried by a head arm assembly (HAA) that includes an actuator arm and a suspension assembly, which can include a separate gimbal structure or can integrally form a gimbal. During operation, as the disc spins, the slider glides above the surface of the disc on a small cushion of air. The actuator arm pivots to movably position the slider with respect to the disc. A microactuator assembly can be included to provide additional precision positioning of the suspension assembly. Electrical connections extend along the suspension to electrically connect the transducing head to components located at or near the actuator arm. Those electrical connections can be formed on the suspension itself, or can be located on a separate interconnect structure supported relative to the suspension, such as a flex-on suspension (FOS).

Magnetic storage media can store data as bit with magnetization directions in-plane, or perpendicular to a plane of the media. Greater storage densities can generally be achieved with perpendicular recording.

The transducing head typically includes a writer and a reader. The reader includes a sensor for retrieving magnetically encoded information stored on the disc. Magnetic flux from the surface of the disc causes rotation of the magnetization vector of a sensing layer or layers of the sensor, which in turn causes a change in the electrical properties of the sensor that can be detected by passing a current through the sensor and measuring a voltage across the sensor. Depending on the geometry of the sensor, the sense current may be passed in the plane (CIP) of the layers of the sensor or perpendicular to the plane (CPP) of the layers of the sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary to recover information encoded on the disc.

The writer, for a perpendicular recording transducing head, typically includes a main pole and a return pole, which are separated from each other at an air bearing surface (ABS) of the transducing head by a gap layer. The main pole and return pole are connected to each other at a region distal from the ABS by a back gap closer or back via. One or more layers of conductive coils are positioned between the main and return poles, and are encapsulated by insulating layers. The conductive coils can have different configurations, such as helical and pancake configurations. To write data to the disc (or other magnetic media), an electric current is applied to the conductive coils to induce a magnetic field in the disc under a pole tip of the main pole. By reversing the direction of the current through the coils, the polarity of the data written to the magnetic storage medium is reversed, and a magnetic transition is written between two adjacent bits of the magnetic storage medium.

The slider includes a slider body (typically called the “substrate”) and an overcoat that includes the transducing head. The overcoat is electrically insulative. A plurality of bond pads are formed on the slider, such as at a trailing edge or top surface of the slider, for electrically connecting elements of the transducing head to external circuitry through the overcoat. There are generally two bond pads for the writer and two for the reader for a given transducing head.

Advances in magnetic recording head technology are driven primarily by a requirement for increased recording density in HDDs. Modern perpendicular magnetic recording heads are approaching a limit in magnetic write fields that can be supplied to write to the perpendicular medium as the density of data tracks written to the magnetic medium becomes larger. Also, as the anisotropy field of the magnetic medium increases, to increase thermal stability the medium, switching fields and media coercivity increase and a stronger magnetic field is required from the perpendicular writer. This places a limit on the density of information that can be stored on a magnetic medium using conventional perpendicular recording heads. Assisted recording techniques have been proposed to introduce extra magnetic fields into the recording media in order to improve the ability of the writer to switch magnetization and record data.

The present invention provides an alternative microwave assisted magnetic recording (MAMR) transducing head design that allows an assist signal to be introduced into a recording medium and facilitates improved writing of information to the recording medium.

SUMMARY

A magnetic writer according to the present invention includes a write element having a write element tip and a conductive structure adjacent the write element. The conductive structure includes two conductive elements positioned substantially parallel to one another and separated by an electrically insulating material. Each of the conductive elements carries a time-varying signal to generate an oscillating magnetic field from a displacement current between the two conductive elements, with the oscillating magnetic field being proximate the write element tip and extending parallel to the air bearing surface. A frequency of the oscillating magnetic field is a function of a frequency of the time-varying signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a transducing head and magnetic storage medium, taken perpendicular to an air bearing surface of the transducing head.

FIG. 2 is an air bearing surface view of the transducing head.

FIG. 3 is a perspective view of write assist elements of the transducing head.

FIG. 4 is a schematic view of a magnetic write assist field generated by the transducing head, shown looking at the air bearing surface.

FIG. 5 is a schematic view of an embodiment of an electrical circuit associated with the transducing head.

FIG. 6 is a schematic view of an embodiment of an electrical circuit associated with the transducing head.

DETAILED DESCRIPTION

In general, the present invention provides ferromagnetic resonance (FMR) assist features for microwave assisted magnetic recording (MAMR) systems. More particularly, the present invention provides a transducing head with a writer having two conductive elements positioned substantially parallel to one another. The two conductive elements are arranged substantially perpendicular to an air bearing surface (ABS) of the transducing head and to a plane of a magnetic recording medium. Each of the conductive elements carries a time-varying current at a frequency greater than about 2 GHz to generate an oscillating magnetic field from a displacement current between the two conductive elements, with a frequency of the oscillating magnetic field being a function of a frequency of the time-varying current. The oscillating magnetic field has a vector component that extends in-plane with the magnetic recording medium. The two conductive elements can be located proximate a write element tip of the writer.

There are two main advantages of MAMR systems. First, as the write pole is reduced in dimension to record data tracks on the magnetic storage medium at higher densities, such as those exceeding about 500 Gbit/in², the magnetic field from the pole is reduced. The presence of the microwave frequency magnetic assist field allows the write pole to record data even at reduced write pole dimensions. Second, as magnetic anisotropy of a recording layer of the magnetic storage medium is increased to improve thermal stability and facilitate improvements in data linear densities recorded to the magnetic storage medium, the switching field of the magnetic storage medium increases and the ability of a given write pole to switch the media magnetization decreases. The microwave frequency magnetic assist field reduces the switching field of this high anisotropy magnetic storage medium and allows the writer to record data. In short, the use of microwave frequency magnetic assist fields yields improvements in the capability of the writer to write at higher track densities and higher linear densities.

FIG. 1 is a schematic cross-sectional view of a disc (or other magnetic storage medium) 22 and a transducing head 40, taken perpendicular to an ABS 42 of the transducing head 40. For simplicity, no cross-hatching is shown in FIG. 1. The transducing head 40 can be carried by the slider 32. The disc 22 includes a layer of recording material 44 that faces the transducing head 40, in which data tracks 36 are defined. In modern hard disc drives (HDDs), the layer of recording material 44 can comprise an alloy of CoPt, Co—Cr—Pt—SiO₂, etc. In one embodiment, the disc 22 and the transducing head 40 are configured for perpendicular recording, but in alternative embodiments can be longitudinal or tilted in configuration.

The transducing head 40 includes a reader assembly and a writer assembly. The reader assembly includes a read element 46 positioned between a pair of shields 48. It should be noted that the reader assembly is optional, and is not required for the present invention. The writer assembly includes a write pole 50 having a write pole tip 52, a coil 54, and a MAMR subassembly 56. The write pole 50 can be arranged substantially perpendicular to the ABS 42 of the transducing head 40, and can comprise a high moment magnetic material.

The MAMR subassembly 56 includes a pair of write assist elements (collectively designated by reference number 58), and corresponding pairs of interconnect traces 60 and electrical connection pads 62. The write assist elements 58 extend substantially parallel to one another in a generally coplanar configuration, and are arranged substantially perpendicular to the ABS 42 of the transducing head 40. In the illustrated embodiment, the pair of write assist elements 58 are arranged substantially parallel to the write pole 50. The write assist elements 58 each comprise an electrically conductive material, such as Cu, Au, or other suitable materials. Each of the write assist elements 58 is electrically connected to one of the interconnect traces 60 at a location distal from the ABS 42, and the interconnect traces 60 are each connected to a corresponding electrical connection pad 62 that provides an external terminal for connecting the MAMR subassembly 56 to external circuitry. It should be noted that only one of each of the element pairs in the MAMR subassembly 56 are visible in FIG. 1.

The transducing head 40 further includes an electrically insulating material 64 that surrounds internal components of the head 40. For instance, the electrically insulating material 64 extends between the pair of write assist elements 58. It should be noted that in further embodiments the transducing head 40 can include additional features not shown in FIG. 1, and the configuration of the transducing head 40 can vary in alternative embodiments. For example, additional electrical connection pads (not shown) for the writer, reader, heater elements, etc. can be provided. Moreover, the configuration and location of the coil 54 can vary as desired for particular applications.

FIG. 2 is an ABS view of the transducing head 40. In the illustrated embodiment, the pair of write assist elements 58 is identified as first and second write assist elements 58A and 58B, respectively. The first and second write assist elements 58A and 58B can have substantially identical sizes and shapes. In the illustrated embodiment, the first and second write assist elements 58A and 58B each extend to the ABS 42 and are each shaped like rectangular boxes, though it should be understood that other shapes are possible on alternative embodiments. As shown in FIG. 2, the first and second write assist elements 58A and 58B are spaced from one another by a gap G, with the electrically insulating material 64 filling the gap G. The gap G can be about 10-5,000 nm, or between about 500-1,000 nm. In one embodiment, the gap G is about 500 nm. The first and second write assist elements 58A and 58B are spaced from a trailing edge of the write pole 50 in an on-track direction, with the write pole tip 52 located in between the reader and the first and second write assist elements 58A and 58B. The write pole tip 52 can be substantially aligned with a midpoint of the gap G. The first and second write assist elements 58A and 58B each have a thickness T in the on-track direction. The thickness T can be about 5,000 nm or less, or about 700 nm to about 5,000 nm. In one embodiment, the thickness T is about 5 microns. Widths of the first and second write assist elements 58A and 58B in the cross-track direction can vary as desired for particular applications, and are not as significant as the thickness T for operation. In the illustrated embodiment, lengths of the first and second write assist elements 58A and 58B (measured perpendicular to the ABS 42) are commensurate with that of the write pole 50.

A stronger magnetic assist field is generally desirable. The strength of the magnetic assist field varies as a function of the gap G and the thickness T. It was discovered through testing that greater values of the thickness T and smaller values for the gap G tend to produce stronger magnetic assist fields.

The transducing head 40 can be manufactured using known techniques, such as photolithography, trench patterning, etc.

FIG. 3 is a perspective view of the first and second write assist elements 58A and 58B of the transducing head 40, shown in isolation (i.e., other portions of the transducing head 40 are not shown). As shown in FIG. 3, a time-varying oscillating electrical signal S is applied to the first and second write assist elements 58A and 58B such that a current I is applied along the length of each of the first and second write assist elements 58A and 58B. The oscillating electrical currents I are discussed further below. The oscillating electrical currents I generate a time-varying electric field between the first and second write assist elements 58A and 58B, illustrated in FIG. 3 by solid arrows. As the time-varying electric field passes along the first and second write assist elements 58A and 58B, a displacement current passes between the first and second write assist elements 58A and 58B. The displacement current generates a time-varying oscillating magnetic assist field, illustrated in FIG. 3 by dashed arrows. The time-varying oscillating magnetic field passes between the first and second write assist elements 58A and 58B in a direction perpendicular to the time-varying electric field and in a direction parallel to the first and second write assist elements 58A and 58B. As shown in FIGS. 1 and 2, the oscillating magnetic field has a vector component 66 oriented substantially parallel to the ABS 42, perpendicular to the first and second write assist elements 58A and 58B, and in-plane with the layer of recording material 44 of the disc 22. It was found through testing that the overall oscillating magnetic assist field produced by the MAMR subsystem 56 was dominated by the vector component 66 of the magnetic assist field (or FRM field) in the on-track direction, and cross-track and perpendicular components were negligible in comparison (see FIG. 4). In particular, a peak magnitude of the magnetic assist field tends to occur at the midpoint of the gap G between the first and second write assist elements 58A and 58B (see FIG. 4).

The oscillating magnetic assist field can be placed over a magnetic field 68 produced by the write pole 50, and can extend to an adjacent portion of the disc 22 to assist with recording proximate the trailing edge of the write pole 50 (see FIG. 1). The oscillating magnetic assist field is introduced into the layer of recording material 44, reducing a media switching field and improving the ability of the writer to record data to the disc 22.

The oscillating magnetic assist field vector component 66 is perpendicular to magnetic moments of bits defined in the layer of recording material 44 of the disc 22, and exerts a torque on those magnetic moments. This torque causes the magnetic moments of the bits to tilt and rotate off axis. At certain frequencies, the torque exerted on the layer of recording materials 44 will cause the magnetization moments to resonate with the applied signal. A frequency of FMR for the layer of recording material 44 typically occurs in a range of about 2-100 GHz for materials typically used in modern HDDs, and more particularly within a range of about 10-50 GHz for preferred materials of the layer of recording material 44. The particular frequencies at which FMR occurs is a function of material properties. It should be noted that previous generation HDDs utilized different compositions of recording materials, which generally experience FMR effects in different frequency ranges than the materials used in modern HDDs.

In a recording system the magnetic assist field is introduced into the layer of recording material 44 as the write pole 50 attempts to switch the magnetization of a given bit in order to record information to the disc 22. The magnetic assist field can be applied to a large area of the recording layer, as the magnitude of the magnetic assist field alone is generally not large enough to switch the media magnetization, that is, the magnetic assist field alone is generally unable to write to the disc 22. Switching of bits on the disc 22 occurs only when a magnetic field from the write pole 50 is applied. However, the FMR effect produced by the magnetic assist field lowers the magnetic switching field of the layer of recording material 44, which facilitates easier switching of media magnetization and allows easier writing of data bits to the disc 22. The ability of the write pole 50 to record information to the disc 22 is therefore improved without increasing widths of the data tracks 36, and effective writing is possible even with relatively small track widths and a relatively small transducing head 40.

FIG. 4 is a schematic view of the magnetic write assist field generated by the transducing head 40, shown looking at the ABS 42. As shown in FIG. 4, arrows represent magnetization vector components of the magnetic write assist field. Although not specifically shown in FIG. 4, the first and second write assist elements 58A and 58B are located at left and right sides of the figure, with the gap G located in approximately the center of the figure. The relatively large concentration of magnetization vectors in the center of FIG. 4 correspond to a peak magnitude of the oscillating magnetic assist field that tends to occur at the midpoint of the gap G between the first and second write assist elements 58A and 58B.

FIG. 5 is a schematic view of an electrical circuit associated with the transducing head 40 that includes a preamplifier 80 and a flex circuit 82. The disc 22 is shown in FIG. 5 for reference. Also, the pads 62 are separately identified as first and second pads 62A and 62B, respectively, in FIG. 5. In the illustrated embodiment, the preamplifier 80 includes a DC power supply 84 electrically connected to an oscillator circuit 86. The preamplifier 80 can generally be of a conventional design, and the oscillator circuit 86 can be configured to produce a desired oscillation frequency, as discussed further below. The preamplifier 80 is electrically connected to the flex circuit 82, which in turn is electrically connected to the first and second pads 62A and 62B, respectively. The flex circuit 82 can be of a conventional configuration, and can be any structure capable of transmitting electrical signals along a suspension between the transducing head 40 and the remotely located preamplifier 80. The oscillator circuit 86 creates time-varying signals for each of the first and second write assist elements 58A and 58B that pass through the flex circuit 82 to the first and second pads 62A and 62B, and from the first and second pads 62A and 62B to the first and second write assist elements 58A and 58B, respectively. In this way, time-varying signals are generated outside of the transducing head 40 and are transmitted to the first and second write assist elements 58A and 58B in the transducing head 40 in order to generate a microwave frequency magnetic write assist field as described above.

The time-varying signals generated by the oscillator circuit 86 can have a given amperage (e.g., less than or equal to about 50 milliamps) and a time-varying voltage (e.g., about 2-10 V DC). Alternatively, the time-varying signals generated by the oscillator circuit 86 can have a given voltage and a time-varying amperage. The particularly frequency of the time-varying signal can be selected as a function of material properties of the layer of recording material 44 in the disc 22, which is to say that that the frequency of the time-varying signal is selected so as to produce an FMR effect in the layer of recording material 44 in the disc 22 as a result of the oscillating magnetic assist field generated from the time-varying signal. Greater voltages will generally produce greater magnetic assist fields, which is typically desirable. It should be noted that there may be a maximum desirable current density for particular applications, in order to reduce a risk of damage to the transducing head 40 during operation.

It should be understood that the particular frequency of signal oscillation, the signal amplitude, and other parameters can vary for particular applications. Optimal values can vary as a function of the structural, electrical and magnetic characteristics of a given transducing head 40. The frequency of the oscillating signal is generally greater than about 2 GHz, which is a range of frequencies greater than those associated with prior art wire system magnetic recording

FIG. 6 is a schematic view of an alternative embodiment of an electrical circuit associated with a transducing head 140 including a preamplifier 180 and a flex circuit 82. The configuration and operation of the electrical circuit illustrated in FIG. 6 is generally similar to that described above with respect to FIG. 5. However, in the electrical circuit of FIG. 6 an oscillator circuit 186 is located within the transducing head 140 rather than within the preamplifier 180. In this way, non-oscillating DC currents are directed from the preamplifier 180 through the flex circuit 82 to the transducing head 140. Time-varying signals are generated inside the transducing head 140 and are transmitted to the first and second write assist elements 58A and 58B in the transducing head 40 in order to generate a magnetic assist field as described above.

Those of ordinary skill in the art will recognize that the present invention provides numerous advantages. For example, the present invention provides an alternative MAMR system that can produce suitable magnetic assist fields with on-track field strengths focused in desired locations on an adjacent magnetic storage medium.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, the particular configuration of reader and writer elements in a transducing head according to the present invention can vary as desired for particular applications. 

1. A magnetic writer comprising: a write element including a write element tip positioned at an air bearing surface; and a conductive structure adjacent the write element, wherein the conductive structure comprises two conductive elements positioned substantially parallel to one another and separated by an electrically insulating material, wherein each of the conductive elements carries a time-varying signal to generate an oscillating magnetic field from a displacement current between the two conductive elements, wherein the oscillating magnetic field is proximate the write element tip and extends parallel to the air bearing surface, and wherein a frequency of the oscillating magnetic field is a function of a frequency of the time-varying signal.
 2. The magnetic writer of claim 1, wherein the two conductive elements are arranged substantially parallel to the write element.
 3. The magnetic writer of claim 1, wherein each of the two conductive elements are wires having a thickness in an on-track direction of less than or equal to about 5 microns.
 4. The magnetic writer of claim 1, wherein the conductive structure is located adjacent a trailing edge of the write element tip.
 5. The magnetic writer of claim 1, the time-varying signal has a frequency greater than 2 GHz.
 6. The magnetic writer of claim 1, wherein the conductive structure carries the time-varying signal at a frequency between about 10-50 GHz.
 7. The magnetic writer of claim 1, wherein the time-varying signal carried by the conductive structure varies in voltage.
 8. The magnetic writer of claim 1, wherein the time-varying signal carried by the conductive structure is less than or equal to about 50 milliamps.
 9. A magnetic storage assembly comprising: a magnetic storage medium defining a recording layer in a plane; and a transducing head positioned adjacent to the magnetic storage medium, the transducing head comprising: a write element including a write element tip; and a conductive structure adjacent the write element, wherein the conductive structure comprises two conductive elements positioned substantially parallel to one another, wherein each of the conductive elements carries a time-varying current to generate an oscillating magnetic field at a magnetic resonance frequency of the recording layer of the magnetic storage medium, and wherein the oscillating magnetic field extends in-plane with the recording layer of the magnetic storage medium.
 10. The assembly of claim 8, wherein the oscillating magnetic field is developed by a displacement current between the two conductive elements.
 11. The assembly of claim 8, wherein the two conductive elements are arranged substantially perpendicular to an air bearing surface of the transducing head.
 12. The assembly of claim 8, wherein each of the two conductive elements are wires having a thickness in an on-track direction of less than or equal to about 5 microns.
 13. The assembly of claim 8, wherein the conductive structure is located adjacent a trailing edge of the write element tip.
 14. The assembly of claim 8, wherein the conductive structure carries the time-varying current at a voltage that varies at a frequency between about 10-50 GHz.
 15. The assembly of claim 8, wherein the time-varying current carried by the conductive structure is less than or equal to about 50 milliamps.
 16. A method of writing to a magnetic storage medium having a recording layer arranged in a plane, the method comprising: generating a time-varying electric field between a pair of write-assist elements to generate an oscillating magnetic field in-plane with the recording layer of the magnetic storage medium at a frequency that causes magnetic resonance in the recording layer; and generating a magnetic recording field in a write pole located adjacent to the write-assist structure.
 17. The method of claim 15, wherein the time-varying electric field generates a displacement current between two substantially parallel conductive elements of the write-assist structure.
 18. The method of claim 15, wherein the conductive elements each carry a time-varying current at a voltage that varies at a frequency greater than 2 GHz.
 19. The method of claim 15, wherein the conductive elements each carry a time-varying current at a voltage that varies at a frequency between about 10-50 GHz.
 20. The method of claim 15, wherein a time-varying signal applied to the conductive elements is less than or equal to about 50 milliamps. 